The invention concerns an apparatus for the manufacture of pressed articles from plastic material, with which the output of articles produced per unit may be varied within wide limits without varying the production time per piece and thus departing from the optimum method of procedure and tool utilization in the individual steps of the operation.
The sequence of operations in the pressing of plastic material, such as glass for example, consists essentially of charging, pressing, solidification and discharging. These steps ought to follow one upon the other insofar as possible, without unnecessary waiting during one of the four operations due to another which takes longer to perform with the result that some of the tools will not be utilized in an optimum manner. However, even where the production procedure is optimized for the individual piece and is to remain unchanged, it ought to be possible to vary the output of the press. These requirements are not fulfilled by machines of the prior art.
In known, intermittently driven round-table presses having one pressing station, the cycle time is determined by the actual pressing as the longest, indivisible operation, resulting in waiting time in the other working stations. Furthermore, to each operation must be added the time required for the table transport, so that in general such presses can achieve only relatively low outputs.
In a continuously circulating press in which each station is equipped with a plunger, a ring and a mold, more tools are installed than would be necessary if tool utilization were optimum.
In presses such as those described, for example, in German Pat. No. 964,093 or in U.S. Pat. No. 2,009,994, in which the plungers and rings are stationary and the molds circulate individually, i.e., without being joined together by a table, the output is just as limited by the at least partially intermittent movement of the molds as it is in the intermittently driven round-table press.
Another aspect of the invention involves the transportation system. Automatic systems have been developed in which the individual workpiece is no longer made at one place by a series of tools engaging it, but instead the workpiece is advanced from one working state to the next by a suitable conveyor member, the individual working steps being able to be set up in a single machine unit or divided among a plurality of machines set up in sequence to form an automatic production system.
In known machines of this kind the conveyor member which functionally interconnects the individual working stages consists of holding means, chucks or the like, in which the workpieces are held for working, and which are joined together by stiff or partially resilient intermediate members to form an endless chain-like structure which circulates in suitable guides within the automatic manufacturing system. It is required that this chain-like structure have a constant division-- i.e., that these holding means, chucks or the like be at the same distance from one another.
These known machines may operate in two different ways: either the chain-like conveyor means holding the workpieces advance continuously at constant velocity or they are driven intermittently. In any case, however, the circulation of all workpiece holding means is synchronous.
In the case of intermittent operation the conveyor means and thus also the workpieces are at a standstill during the working procedures which accordingly are performed with stationarily disposed tools. Upon completion of a working procedure the conveyor means moves the workpieces synchronously to the next-following working station and then stops. The division of the conveyor means, i.e., the distance between two successive workpieces, is governed in this method of operation by the spatial dimensions of the largest working station. The spacing at all the rest of the working stations must accordingly be an integral multiple of the required conveyor means spacing; for this reason optimum utilization of floor space is not possible and the automatic system becomes relatively large. The standstill time of the conveyor means during the working is governed by the longest working procedure, so that the tools in the other working stations are not fully utilized time-wise. Another disadvantage of intermittent operation lies in the relatively high acceleration forces which are exerted on the workpieces when the conveyor means is started and stopped. These forces are capable, for example, of deforming freshly blown or cast, still-hot parisons.
The disadvantages caused by the acceleration forces, may be largely avoided by the continuous method of operating the conveyor means. Here the only acceleration forces are radial forces where the direction of the path of movement changes. In the continuous method of operation, in which the conveyor means circulates with uniform velocity, the working tools must be positively propelled together with the conveyor means and hence with the workpiece over certain distances corresponding to the duration of the particular operation. As mentioned, if this is done by means of round tables, for example, on which a plurality of working procedures are performed, each station must necessarily be provided with the tools for all these procedures, which means an extremely poor time-wise utilization of the tools. The spacing of the conveyor means is determined in these known machines by the operation that takes the longest amount of time, and thus it results in further poor time-wise utilization of all those tools whose engagement is required for only a relatively short amount of time. In this respect, continuously operating and intermittently operating machines have similar disadvantages.
In both of the known types of machines the velocity of transport and hence the output of glassware is limited by the fact that in certain working steps the acceleration forces involved in movement lead to difficulties and therefore may not exceed a certain value.
In addition to the indicated disadvantages of the known processes it is therefore impossible, where the end products must fulfill certain quality requirements, to increase the output by increasing the overall speed of the system, because in this case technological limits are reached in different working stations. In this connection, it is possible that it may be technologically very desirable in an otherwise continuous method of operation to bring the workpiece even to a full stop in some of the working stations.
A method of transporting glass material in the piece-by-piece production of glassware ought therefore to be such, in order to avoid the above-described disadvantages, that a great output per unit will be achieved while allowing sufficient time for the individual procedures, and with an acceptable investment in well-utilized tools without allowing the velocity of transportation to increase at any point to technologically undesirable or unacceptable values. The amount of space is to be kept small, and the timing of the transport is to be variable for adaptation to a variety of manufacturing procedures or to a variety of tool combinations to meet the requirements of various products, without thereby greatly reducing the utilization of individual tools. The transport system must also permit the interchange of complete machine units involving a plurality of working stations.